The present invention relates to gas turbine engines and, more particularly, relates to apparatus for ducting bleed air from the compressor section of the engine through ventilated blades on the turbine rotor.
In gas turbine engines a fluid working medium such as air is ingested into the compressor section of the engine and is delivered at an elevated pressure to a combustion section where the air combines with fuel in a combustion process. The products of combustion are hot gases which are discharged at high velocity over the blades of rotors in the turbine section where some or most of the dynamic velocity is converted into mechanical power before the gases are exhausted or expelled for propulsion. Power developed from the turbine rotors is utilized to drive the compressor and any associated power-consuming equipment such as an aircraft propeller or an electrical generator.
Since the combustion gases reach elevated temperatures which even the finest metals may not withstand over long periods of time, it is well known to provide apparatus for cooling the turbine blades during engine operation. The typical cooling apparatus bleeds a portion of the air in the flow path through the compressor at pressures which are slightly above the working pressure of the hot gases moving through the turbine blades. The bleed air is conducted through passageways within a non-rotating environment of the engine and are transmitted to the rotating environment of the turbine blades by means of a fluid pump.
U.S. Pat. Nos. 2,988,325 to Dawson, 3,602,605 to Lee, 3,768,921 to Brown et al and 3,936,215 to Hoff show examples of several prior art pumping devices which transmit compressor bleed air from a rotating to a non-rotating environment for cooling blades in the turbine section of the engine.
Since the hot combustion gases in the current state of the art enter the turbine section at approximately 94% of the compressor exit pressure, it is essential that the bleed air be delivered to ventilated turbine blades without substantial pressure loss. Otherwise, the flow of bleed air may be severely restricted or stalled, and the cooling or other function performed by such air will be impaired or lost. The pumping apparatus disclosed in the Brown U.S. Pat. No. 3,768,921 for transferring the bleed air from the rotating to the non-rotating environment attempts to maximize the static pressure developed within the turbine section by producing a free vortex flow in a non-rotating chamber from which the cooling air passes into the turbine rotor and blades. The other patents referenced above direct bleed air in a tangential direction to a series of annular apertures on the rotor without attempting to recover the total static pressure of the bleed air, or any loss of dynamic pressure is minimized by matching the tangential velocity of the air with the rotor speed. Since the maximum tangential velocity yields the minimum coolant temperature, matching the velocity with rotor speed imposes an inherent limitation on the cooling system.
It is a general object of the present invention to obtain the maximum static pressure for bleed air in a turbine rotor by an improved pumping apparatus that transfers the air from nonrotating to rotating environments. It is a further object of the invention to be able to maximize the velocity of tangentially transferred bleed air for a minimum coolant temperature.